You can tell me your preference for litter and I will note that, but most pups will be chosen closer to 7 weeks of age. As each litter is tested at 7 weeks of age, I will offer pups to those who are first in line, second in line, and so on down the list. When they have chosen a puppy they will be removed from the list.
When you are notified about choosing a puppy, you will have up to 24 hours to decide which puppy you want or to pass on the litter and wait for the next one. You cannot wait to decide until after all of the litters have turned 7 weeks because that would take too long to get puppies chosen. If you have questions feel free to ask!